Bashiok
The Invite-A-Friend keys were only sent to active participants in the beta.  The cutoff was that participants had logged in within the last three weeks.

Outside of that we did identify issues with the process and some people did not receive keys who should have.  We'll be correcting that and sending those emails out soon.  Likely within the next day or two.

We are also evaluating potentially sending out more Invite-A-Friend emails with different activity requirements.

edit: Additionally it should be mentioned that you ensure to check all spam and/or junk mail boxes to ensure the email wasn't filtered as such for you.